A plurality of functions are being increasingly integrated in coolant systems, especially for motor vehicle air conditioning systems, which entail high demands on the individual components of the particular coolant system. For example, a heat pump functionality is being increasingly provided in the design of coolant systems for motor vehicles. The components used in this case, especially the valves and the expansion elements, have to be outfitted with increased functions. For example, the valves have to be designed to be bidirectional with regard to the flow direction of the coolant.
Expansion valves arranged in a coolant circuit, by a locally designed narrowing of the flow cross section, are used for a reduction of the pressure of the flowing coolant and thus, a volume increase or an expansion of the coolant. The expansion valve is arranged in the coolant circuit upstream from the evaporator, so that the compressed liquid coolant expands into the evaporator. Thus, the expansion valve forms the interface between the high-pressure side and the lower-pressure side of the coolant circuit, which furthermore has at least one compressor and one condenser downstream from the evaporator in the direction of flow of the coolant.
Traditional ball valves have a servo drive, which drives a shaft mounted in a shaft bearing. The shaft transmits the rotary motion to a valve element, which is configured as a ball with a through channel. The components are mounted inside a valve housing. Ball valves are considered to be robust and economical and they are used for diverse applications.
FIG. 1 shows the cross section of a familiar ball valve 11 of the prior art in simplified form. The ball-shaped valve element 12 is arranged inside a housing 13 and able to turn about an axis of rotation 17. The valve element 12 has a through channel 16 and the housing 13 has a flow channel 14. In the at least partly opened position of the valve element 12 in regard to the flow channel 14 of the housing 13, the fluid flows through the ball valve 11 in the direction of flow 15.
In the arrangement of the ball valve 11 shown in FIG. 1, the ball-shaped valve element 12 is rotated within the housing 13 such that a minimum flow opening is adjusted for the fluid. Two minute openings 18a, 18b are formed at the entrance to the through channel 16 and at the exit from the through channel 16, respectively. When the ball valve 11 is installed inside a coolant circuit, these small openings act as expansion cross sections 18a, 18b. The coolant is expanded both when flowing through the first expansion cross section 18a and when flowing through the second expansion cross section 18b. Since a vapor phase is formed during the expansion process, especially after the expansion cross section 18a, the flow cross section is blocked. A correct regulating of the coolant mass flow by adjusting the valve element 12 of the ball valve 11 is not possible.
DE 10 2007 025 516 A1 discloses a ball cock for shutting off and opening a pipeline in controlled manner The ball cock has a housing with a housing inlet and a housing outlet, also a valve ball with entry openings and an exit opening, as well as an outside activated adjusting device for turning the valve ball around its axis of rotation. The cross section of the exit opening is symmetrical to a plane oriented with the center axis of the entry opening and perpendicular to the axis of rotation. The ball has a third circular opening, whose axis lies in the plane of symmetry and intersects the center axis of the entry opening at right angles. With the help of the described ball cock, the regulation of the flow rate of fluids is improved and in particular it becomes linear over a larger range, experiencing no phase change upon flowing through the ball cock.
However, few suitable components are available in the prior art for use in a coolant circuit, so that there is a need to modify existing components and adapt them to the new chores. In particular, with the ball valves known in the prior art, no precise regulation of the mass flow of coolant is possible, especially on account of the unwanted expansion and evaporation of the coolant upon flowing through the ball valve.